This invention relates in general to transports for sheets of material and in particular, to detecting the wrinkling of the sheets.
Document scanners, copiers, fax machines, photographic film machines and newspaper processing machines use feeders to transport sheets of material. Mechanisms used for the transportation of the sheets of material, which may include paper, documents, film, etc., have the capacity to wrinkle these sheets. It is necessary to determine when a sheet of material starts to wrinkle in a transport so the transport may be stopped quickly before the sheet is damaged.
The present methods used to detect jams and wrinkling of sheets of material involve measuring the time the sheet of material takes to move through the transport. Various check points are distributed along the transport. During normal processing, the sheet is expected to pass these check points at specified times. If the sheet is late arriving at one of these checkpoints used for timing, the assumed there is a jam, the sheet is wrinkling or another error has occurred. The document transport is then stopped. The timing method does not stop transport of the sheet quickly and normally results in one or more documents being seriously damaged or a serious jam with possible physical damage to the sheet of material or transport.
In solving a related problem with transports for sheets of material, ultrasonic signals are used to detect feeding multiple sheets with the transport. This non-contact method for the detection of feeding multiple sheets with a transport sends ultrasound signals through the document while monitoring the ultrasound after it has passed through the document. Sending ultrasound through sheets of material, for example, paper, results in attenuation and phase shift of the ultrasound signal. It is possible to determine the feeding multiple documents by measuring the phase shift and/or amplitude of the ultrasound signal passing through documents. For example, U.S. Pat. No. 4,006,969, which is incorporated herein by reference, describes an apparatus for detecting multiple sheets using ultrasound. As ultrasound passes from a ultrasonic transmitter through the documents and to an ultrasonic receiver, the phase of the signal changes, depending on the wavelength and the distance. Ultrasonics offers the advantage of making no contact with the paper and being relatively independent of the paper thickness.
Accordingly, there is a need for a method and apparatus that can detect wrinkling of a sheet of material independent of the sheet thickness. Also, there is a need for a system which can quickly detect a jam or wrinkling of a sheet of material before the sheet is seriously damaged. The method and apparatus should also allow the detection of wrinkling at the leading edge of the sheet as its starts to wrinkle.
A method and apparatus for detecting wrinkling of sheets of material is provided. A signal can be transmitted through the sheet. After the signal has passed through the sheet, it is received by, for example, a receiver. The generated signal may then be compared to the received signal. Wrinkling in the sheet can be determined based on the comparison.
In an exemplary embodiment, a document transport system transports a document along a feed path. A desired angle the document forms with the feed path during normal operation can be determined. An actual angle the document forms with the feed path may also be determined. A difference between the desired angle and the actual angle can then be determined. A document jam in the transport system may be detected when the difference exceeds a predetermined threshold.
In a further embodiment, a sheet is fed along a feed path with a mechanism. A signal may be transmitted through the sheet as it passes along the feed path. The signal is received after it passes through the sheet. A phase difference between the transmitted signal and the received signal can be detected. Also, an amplitude difference between the transmitted signal and the received signal can be detected. Wrinkling of the sheet can be determined based on at least one of the phase difference and the amplitude difference. If wrinkling is detected, the feeding of the sheet should be halted.
According to one embodiment of the present invention, an apparatus for the detection of wrinkling documents comprises an ultrasonic transmitter for transmitting an ultrasonic signal. An ultrasonic receiver receives the ultrasonic signal, which passes through the document in the document transport. A phase comparator compares the transmitted ultrasonic signal and the received ultrasonic signal, and an amplitude measurement circuit compares the received ultrasonic signal to a reference. A microprocessor compares an information signal from the phase comparator and an information signal from the amplitude measurement circuit to a threshold to determine if the document is starting to wrinkle.
This invention can use both phase shift and amplitude variation of ultrasound passed through a document stream to determine start of the wrinkling of a document. By using both phase shift and amplitude of the signal, the start of a wrinkling can be accurately detected. Using ultrasonics allows this information to be determined without physically contacting the paper.
This invention can offer the advantage of making no contact with the paper. By using both the phase and amplitude change of the received ultrasound, the start of the wrinkling of a document can be detected more reliably than is possible by using phase detection alone or amplitude detection alone. It is possible to implement this invention using only the phase or the amplitude detection.